NED Abstract

Copyright by Royal Astronomical Society.
1999MNRAS.306..857C
The ROSAT Brightest Cluster Sample D III. Optical spectra of the central
cluster galaxies
C. S. Crawford, S. W. Allen, H. Ebeling, A. C. Edge and A. C. Fabian
Accepted 1999 February 16 Received 1998 December 21
ABSTRACT
We present new spectra of dominant galaxies in X-ray-selected clusters of
galaxies. which combine with our previously published spectra to form a
sample of 256 dominant galaxies in 215 clusters. 177 of the clusters are
members of the ROSAT Brightest Cluster Sample (BCS; Ebeling et al.), and 17
have no previous measured redshift. This is the first paper in a series
correlating the properties of brightest cluster galaxies and their host
clusters in the radio, optical and X-ray' wavebands.
27 per cent of the central dominant galaxies have emission-line spectra,
all but five with line intensity ratios typical of cooling flow nebulae. A
further 6 per cent show only[N II]{lambda}{lambda}6548, 6584 with H{alpha}
in absorption. We find no evidence for an increase in the frequency of line
emission with X-ray luminosity. Purely X-ray-selected clusters at low
redshift have a higher probability of containing line emission. The
projected separation between the optical position of the dominant galaxy
and its host cluster X-ray centroid is less for the line-emitting galaxies
than for those without line emission, consistent with a closer association
of the central galaxy and the gravitational centre in cooling flow
clusters.
The more H{alpha}-luminous galaxies have larger emission-line regions
and show a higher ratio of Balmer to forbidden line emission, although
there is a continuous trend of ionization behaviour across four decades in
H{alpha} luminosity. Galaxies with the more luminous line emission
[L(H{alpha}) > 10 erg s^-1^] show a significantly bluer continuum, whereas
lower luminosity and [N II]-only line emitters have continua that differ
little from those of non-line-emitting dominant galaxies. Values of the
Balmer decrement in the more luminous systems commonly imply intrinsic
reddening of E(B - V) ~ 0.3 and, when this is corrected for, the excess
blue light can be characterized by a population of massive young stars.
Several of the galaxies require a large population of 0 stars, which also
provide sufficient photoionization to-produce the observed H{alpha}
luminosity. The large number of lower mass stars relative to the 0-star
population suggests that this anomalous population is caused by a series of
starbursts in the central galaxy.
The lower H{alpha}-luminosity systems show a higher ionization state and
few massive stars, requiring instead the introduction of a harder source of
photoionization, such as turbulent mixing layers. or low-level nuclear
activity. The line emission from the systems showing only [N II] is very
similar to low-level LINER activity commonly found in many normal
elliptical galaxies.
Key words: surveys - galaxies: clusters: general - cooling flows-galaxies;
elliptical and lenticular cD - galaxies: stellar content-X-rays: galaxies.